1. Field of the Invention
This invention relates to a control system for an internal combustion engine, including an exhaust gas recirculation system for recirculating part of exhaust gases into an intake passage.
2. Description of the Prior Art
As is widely known, an exhaust gas recirculation system recirculates part of exhaust gases into an intake passage under predetermined operating conditions of an internal combustion engine, for reduction of NOx in the exhaust gases and improvement of fuel consumption. Accordingly, when the exhaust gas recirculation system is operated, carbon and hydrocarbons contained in the exhaust gases flow through an exhaust gas recirculation valve and a recirculation port, so that clogging or partial clogging of the valve and the port can be caused which is a major factor causing flow rate degradation or lowering of an exhaust gas recirculation system including the exhaust gas recirculation valve and the recirculation port. Conventionally, an apparatus for determining abnormality of the exhaust gas recirculation valve has been proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 7-180615. In the determining apparatus, the exhaust gas recirculation valve is opened when fuel supply is cut off during deceleration of the engine, and the intake pipe pressure is detected before and after the opening of the valve. If the amount of change in the intake pipe pressure occurring between before and after the opening is below a predetermined value, it is determined that the exhaust gas recirculation valve is in an abnormal condition. Further, in the determining apparatus, when it is determined that the abnormality of the valve has occurred, exhaust gas recirculation control is kept suspended until the cause of the abnormality is eliminated.
As described above, in the conventional abnormality-determining apparatus, whether the exhaust gas recirculation valve is normal or abnormal is determined by comparing the detected amount of change in intake pipe pressure between before and after the opening of the valve with the predetermined value. However, the intake pipe pressure is susceptible to influences of various factors, such as the pumping capacity (rotational speed, atmospheric pressure, amount of overlap between intake and exhaust valves, etc.) of the engine and an intake opening area (opening of a throttle valve opening of a secondary intake valve, and a master vac of a brake, etc.), and hence it is liable to variation. In particular, it is difficult to grasp the influences of the valve overlap amount and the master vac of the brake on the intake pipe absolute pressure, since there is no suitable means available for detecting them.
For this reason, in the conventional method of determining the abnormality based on simple comparison between the detected amount of change in the intake pipe pressure and the predetermined value, it is difficult to estimate a degree of flow rate degradation of the exhaust gas recirculation system e.g. due to (partial) clogging, which makes it inevitable to carry out rough determination, such as determination of whether the exhaust gas recirculation control valve is normal or abnormal. As a result, even when the ratio of fresh intake air to the whole intake air including the recirculated exhaust gases is increasing under an identical intake pipe pressure in a manner dependent on the progressively increasing degree of flow rate degradation of the exhaust gas recirculation system, the fuel supply control and ignition timing control continue to be carried out in the same manner as when the exhaust gas recirculation valve is normal until the valve is determined to be abnormal, so that the amount of fuel supply and the ignition timing deviate from respective optimum values all the while, which adversely affects exhaust emission characteristics and drivability. Further, since the exhaust gas recirculation valve is also held open to the same degree of opening as in the normal condition until the exhaust gas recirculation valve is determined to be abnormal, if the (partial) clogging of the port due to deposition of carbon and the like on a downstream side of the exhaust gas recirculation valve is responsible for the flow rate degradation, flow load in excess of exhaust gas recirculation capacity continues to be applied to part of the exhaust recirculation passage downstream of the valve. As a result, an increased pressure is applied to the part between the exhaust gas recirculation valve and the recirculation port downstream thereof, which accelerates deposition of carbon, resulting in acceleration of flow rate degradation of the exhaust gas recirculation system.
It is an object of the invention to provide a control system for an internal combustion engine, which is capable of properly controlling the exhaust gas recirculation rate in a manner responsive to flow rate degradation within an exhaust gas recirculation system and at the same time suppressing progress of the flow rate degradation.
To attain the above object, according to a first aspect of the present invention, there is provided a control system for an internal combustion engine having an exhaust gas recirculation system including an exhaust gas recirculation passage for communicating between an exhaust passage and an intake passage, and an exhaust gas recirculation valve for controlling a rate of exhaust gas recirculation to the intake passage via the exhaust gas recirculation passage, according to an operation amount of the exhaust gas recirculation valve.
The control system according to the first aspect of the invention is characterized by comprising:
fuel supply cut-off means for cutting off supply of fuel to the engine during deceleration of the engine;
pressure-detecting means for detecting pressure within the intake passage; and
operation amount-limiting means for setting an upper limit of the operation amount of the exhaust gas recirculation valve according to a change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply.
According to this control system, the exhaust gas recirculation valve is opened and closed during cut-off of fuel supply during deceleration of the engine, and the upper limit of the operation amount of the exhaust gas recirculation valve is set according to a change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed. The change in intake pipe pressure between before and after the opening or closing of the exhaust gas recirculation valve reflects the state of flow rate degradation of the exhaust gas recirculation system including the exhaust gas recirculation passage and the exhaust gas recirculation valve. Therefore, by setting the upper limit of the operation amount of the exhaust gas recirculation valve according to the change in the intake pipe pressure such that the rate of exhaust gas recirculation controlled by the exhaust gas recirculation valve is held within the recirculation capacity of the exhaust gas recirculation system, it is possible to prevent a flow load exceeding the recirculation capacity from being applied to the exhaust gas recirculation system. As a result, the deposition of carbon and the progress of flow rate degradation resulting therefrom can be suppressed. Further, even if flow rate degradation occurs, exhaust gas recirculation control can be carried out without being interrupted, and exhaust gases can be supplied to the intake passage at a limited rate without loss, so that it is possible to properly control the amount of fuel supply and the ignition timing by setting them according to the limited rate of exhaust gas recirculation.
Preferably, the control system further comprises flow rate degradation-estimating means for estimating a degree of flow rate degradation of the exhaust gas recirculation system based on the change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply, and the operation amount-limiting means sets the upper limit of the operation amount of the exhaust gas recirculation valve according to the estimated degree of flow rate degradation of the exhaust gas recirculation system.
According to this preferred embodiment, the flow rate degradation-estimating means estimates a degree of flow rate degradation of the exhaust gas recirculation system based on the change in the pressure within the intake passage detected, and the operation amount-limiting means sets the upper limit of the operation amount of the exhaust gas recirculation valve according to the estimated degree of flow rate degradation. Therefore, since the exhaust gas recirculation rate is set according to the degree of flow rate degradation of the exhaust gas recirculation system, exhaust gas recirculation control can be executed to the maximum possible extent, which enables more appropriate control of the amount of fuel supply and the ignition timing.
Preferably, the control system further comprises operation delay-detecting means for detecting delay in operation of the exhaust gas recirculation valve, and fuel amount-correcting means for correcting an amount of fuel to be supplied to the engine when the exhaust gas recirculation valve is opened such that the amount of fuel is increased as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, delay in operation of the exhaust gas recirculation valve is detected, and when the exhaust gas recirculation valve is opened, the amount of fuel to be supplied to the engine is increased as the detected delay in operation of the value is larger. When the valve is opened, if delay in operation of the exhaust gas recirculation valve is large, the amount of fresh intake air increases with delay in supply of recirculated exhaust gases to cause leaning of the air-fuel mixture. In such a case, by increasing the amount of fuel as described above, it is possible to appropriately control the air-fuel ratio of the mixture supplied to the engine.
Preferably, the control system further comprises operation delay-detecting means for detecting delay in operation of the exhaust gas recirculation valve, and ignition timing-correcting means for correcting ignition timing of the engine when the exhaust gas recirculation valve is opened such that the ignition timing is retarded as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, when the exhaust gas recirculation valve is opened, the ignition timing of the engine is retarded as the detected delay in operation of the valve is larger. If the operation delay is large when the valve is opened, there is a tendency for the amount of fresh intake air to increase, and for the amount of fuel to be increased with the increase in the amount of fresh intake air. As a result, combustion temperature tends to rise, which causes generation of an increased amount of NOx. In such a case, by retarding the ignition timing as described above, it is possible to improve exhaust emission characteristics.
To attain the above object, according to a second aspect of the invention, there is provided a control system for an internal combustion engine having an exhaust gas recirculation system including an exhaust gas recirculation passage for communicating between an exhaust passage and an intake passage, and an exhaust gas recirculation valve for controlling a rate of exhaust gas recirculation to the intake passage via the exhaust gas recirculation passage, according to an operation amount of the exhaust gas recirculation valve.
The control system according to the second aspect of the invention is characterized by comprising:
a fuel supply cut-off module for cutting off supply of fuel to the engine during deceleration of the engine;
a pressure-detecting module for detecting pressure within the intake passage; and
an operation amount-limiting module for setting an upper limit of the operation amount of the exhaust gas recirculation valve according to a change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply.
According to the second aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the control system further comprises a flow rate degradation-estimating module for estimating a degree of flow rate degradation of the exhaust gas recirculation system based on the change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply, and the operation amount-limiting module sets the upper limit of the operation amount of the exhaust gas recirculation valve according to the estimated degree of flow rate degradation of the exhaust gas recirculation system.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control system further comprises a operation delay-detecting module for detecting delay in operation of the exhaust gas recirculation valve, and a fuel amount-correcting module for correcting an amount of fuel to be supplied to the engine when the exhaust gas recirculation valve is opened such that the amount of fuel is increased as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control system further comprises an operation delay-detecting module for detecting delay in operation of the exhaust gas recirculation valve, and an ignition timing-correcting module for correcting ignition timing of the engine when the exhaust gas recirculation valve is opened such that the ignition timing is retarded as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
To attain the above object, according to a third aspect of the invention, there is provided a method of controlling an internal combustion engine having an exhaust gas recirculation system including an exhaust gas recirculation passage for communicating between an exhaust passage and an intake passage, and an exhaust gas recirculation valve for controlling a rate of exhaust gas recirculation to the intake passage via the exhaust gas recirculation passage, according to an operation amount of the exhaust gas recirculation valve.
The method according to the third aspect of the invention is characterized by comprising the steps of:
cutting off supply of fuel to the engine during deceleration of the engine;
detecting pressure within the intake passage when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply; and
setting an upper limit of the operation amount of the exhaust gas recirculation valve according to a change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply.
According to the third aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the method further comprises the step of estimating a degree of flow rate degradation of the exhaust gas recirculation system based on the change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply, and the step of setting an upper limit of the operation amount of the exhaust gas recirculation valve includes setting the upper limit according to the estimated degree of flow rate degradation of the exhaust gas recirculation system.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the method further comprises the step of detecting delay in operation of the exhaust gas recirculation valve, and the step of correcting an amount of fuel to be supplied to the engine when the exhaust gas recirculation valve is opened such that the amount of fuel is increased as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the method further comprises the step of detecting delay in operation of the exhaust gas recirculation valve, and the step of correcting ignition timing of the engine when the exhaust gas recirculation valve is opened such that the ignition timing is retarded as the detected delay in operation of the exhaust gas recirculation valve is larger.
To attain the above object, according to a fourth aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out control of an internal combustion engine having an exhaust gas recirculation system including an exhaust gas recirculation passage for communicating between an exhaust passage and an intake passage, and an exhaust gas recirculation valve for controlling a rate of exhaust gas recirculation to the intake passage via the exhaust gas recirculation passage, according to an operation amount of the exhaust gas recirculation valve.
The engine control unit according to the fourth aspect of the invention is characterized in that the control program causes the computer to cut off supply of fuel to the engine during deceleration of the engine, detect pressure within the intake passage when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply, and set an upper limit of the operation amount of the exhaust gas recirculation valve according to a change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply.
According to the fourth aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the control program further causes the computer to estimate a degree of flow rate degradation of the exhaust gas recirculation system based on the change in the pressure within the intake passage detected when the exhaust gas recirculation valve is opened and closed during the cut-off of fuel supply, and when the control program causes the computer to set an upper limit of the operation amount of the exhaust gas recirculation valve, the control program causes the computer to set the upper limit according to the estimated degree of flow rate degradation of the exhaust gas recirculation system.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control program further causes the computer to detect delay in operation of the exhaust gas recirculation valve, and correct an amount of fuel to be supplied to the engine when the exhaust gas recirculation valve is opened such that the amount of fuel is increased as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control program further causes the computer to detect delay in operation of the exhaust gas recirculation valve, and correct ignition timing of the engine when the exhaust gas recirculation valve is opened such that the ignition timing is retarded as the detected delay in operation of the exhaust gas recirculation valve is larger.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.